Telegraph system with signal testing and error correction



June 29, 1965 H. c. A. vAN DUUREN ETAL 3,192,317

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June 29, 1965 H. c. A. vAN DUUREN ETAL 3,192,317

TELEGRAPH SYSTEM WITH SIGNAL TESTING AND ERROR CORRECTION Filed June 7. 1961 3 Sheets-Sheet 2 H; L. Avlm'fzzzzzzzm; By W1 EHU@ June 29, 1965 H, c. A. vAN DUUREN ETAL 3,192,317

TELEGRAPH SYSTEM WITH SIGNAL TESTING AND ERROR CORRECTION Filed June 7. 1961 3 Sheets-Sheet 3 l-VVI- I .Qu

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United States Patent Ofce 3,192,317 Patented June 29, 1965 3,192,317 f TELEGRAPH SYSTEM WITH SIGNAL TESTING AND ERROR CORRECTION Hendrik Cornelis Anthony van Duuren, Wassenaar, and

Wilhelm Fredrik Brok, Voorburg, Netherlands, assignors to De Staat der Nederlanden, ten deze Vertegen- Woordigd door de Directeur-Generaal der Posterijen, Telegrae en Telefonie, The Hague, Netherlands Filed June 7, 1961, Ser. No. 115,521 Claims priority, application Netherlands, June 9, 1960,

- 252,437 30 Claims. (Cl. 178-23) The invention relates to a telegraph system with error correction by repetition and gradual correction of disturbed signal elements, as well as to a system with element testing and signal testing (Le. constant mark/ space ratio of elements in each signal) connected with it.

In older systems of this kind, signals arriving too early are often lost in repetition cycles, which means loss of information. It has been proposed to store such correctly received signals for further arrangement (see C. I. Van Dalens copending U.S. patent applications Serial Number 773,925 iled November 14, 1958, now U.S. Patent No. 3,001,018 issued September 19, 1961 and Serial No. 115,380 tiled lune 7, 1961, led on even date herewith, both of which copending applications are assigned vto the same assignee).

According to the present invention information is stored by a continued integrating reception, i.e. by storing received signals in analogous memory elements during contingent successive repetition cycles.

Thus according to this invention a telegraph system with error correction by repetition and gradual correction of disturbed signal elements is obtained.

The invention will be explained by a system in which the elements are tested for their graduated quality, as well as the signals built up of those elements. The former test implies that the receiver delivers to analogous memory elements, e.g. capacitors, signal elements as quantities or charges of values gradually rising by the fraction of correct reception per signal element. test implies that the number of digital Values of the signal elements amounts to more than two and contains besides a zero level also a number of graduated intermediate values or classes according to the fractions of correct reception which correspond to the condition of the transmission path.

The annexed drawings illustrate by way of example an embodiment of a telegraph system according to the invention, in which notably:

FIG. l is a schematic block diagramofa high-frequency radio communication system embodying the circuits of this invention; v

FIG. 2 shows a schematic wiring diagram of the discriminating part of the high-frequency circuit shown in FIG. 1, serving to deliver a double-current signal to the scanning system of FIG. 3;

FIG. 3 is a schematic Wiring diagram of the scanning system for one element of a group of multi-element signals of the scanner part of the circuit of FIG. 1 showing capacitors in which'received signals are stored, element testing triggers, and code triggers which form the input circuit for the code converter of FIG. 6;

FIG. 4 shows a schematic block wiring diagram of the distributor part of the circuit of FIG. 1 showing a set of triggers supplying the pulses for controlling the circuits in FIG. 3;

FIG. 5 shows' Wave form diagrams of the shapes and l the time positions of the pulses delivered by the triggers of FIG. 4;

In other terms, the

FIG. 6 is a schematic block wiring diagram of the code converter part of the circuit of FIG. 1; andv FIG. 7 is a general time diagram of the reception of a block of three consecutive seven units signals.

The system shown is of the type working with semisynchronized transmitting and receiving memories, as described in applicants joint copending U.S. patent application Serial No. 94,337, tiled March 8, 1961. It may work otherwise, however, and is notably not tied to block transmission. According to the system of said application, signals are transmitted in blocks of three consecutive, signals followed by a pause during which a return signal can be received. Y v

The system of the present application is essentially a simplex system and it is semi-synchronous, that is normally it works synchronously, but after a disturbance, synchron ism may be re-established by a start signal if necessary.

In FIG. 1 the input part of the present system is assumed to arrive as a frequency-Shift signal, FSK, passing through a band-pass filter 2, a limiter 3 and is altered by a discriminator 4 into a double-current signal U (see FIG. 2), the amplitude of which, in normal working, is e.g. three times the voltage on the capacitors.

With a telegraphic speed of e.g. 100 bauds the frequency shift signal FSK arriving at the input of the circuit of' which are connected in series'to deliver a modulated D.C.

voltage between points 7 and 8.

This D.C. voltage from the leading edge of the first signal element received is applied via point 9, FIG. 4, to the synchronizing device 10 of the distributor circuit to synchronize the apparatus of this invention, and to which device 1t) a series of pulse triggers TP, TQ, TR are connected via a connection 11, as well as a ring counter 12 consisting of triggers RC1, RC2, RC3, RC4 RC2() and RC21 to be extended according to the number 0f elements of a signal; triggers TE, and TF 1 serving finally to control the scanning circuits of FIG. 3.

The bottom line of FIG. 5 shows by way of example the wave form in which the voltage U may appear. Further FIG. 5 shows the wave forms in time diagrams of the pulse series P, Q, R, A, B, C, D, E, F, from triggers In `the example, the duration of a signal element amounts to 10 ms., contained between the leading edges of two Asuccessive R-pulses produced by trigger R. Time in FIG. 5 proceeds from left to righ-t, and, as can be seen, each R-.pulse is preceded by a Q-pulse, which in its y Iturn is preceded by a Ppulse.

The inverse pulses belonging to the pulse system are' indicated by primes; and are not Irepresented in FIG. 5.

The voltage U from discriminator 4 also arrives at'v ,the input terminal of the scanning circuit according to It is successively divided in time over the lcapacltors a, b, etc. The momen-ts when there isa connection between the discriminator 4 youtput terminal and one of the capacitors are determined by charging gate 13 consi-sting of a lcombination of rectiers and resistors `which form together an and gate circuit. Thus the charging vgate for the element A in scanning circuit Y21 n will pra-ss -a'positive voltageirom input U to condenserk a, when the voltage applied to the rectitier marked A13 is positive, which is the case, consequently, when the relevant pulse appears (shown by the pulse on line A in FIG. 5). The same thing applies to' the other capacitors b, c, d, etc. and the other blocks (not shown in FIG. 3),. 'If voltage U' is negative `.in such anv interval, the relevant capacitors a, b, c Y. etc. i-s given a negative charge via the A13 rectiiier in gate 13 'during the inverse A-'periodv In the interval Q the capacitor a voltage is tested via test .gates in Veach unit 14 in common threshold triggers provided in duplicate for each signal element, viz. triggers K+S and K s. The working lof these triggers is suchthat they operate every time a capacitor, e.g. 11,.

proves to be charged to a Voltage higher than the predetermined adjustable threshold in the trigger. A plurality of pairs -of threshold triggers may be associated with each element lscanning circuit 21 corresponding to different voltage levels ror classes for vario-us degrees of security,

so that the threshold can be Vraised if reception is bad` and lowered if .the reception is good, thereby decreasing the number of repetitions needed for getting a complete group signal and consequently saving time in the communication. If after the test neither of triggers KIS and K s has operated, they excite together a zero trigger Ko on the interval of pulse R.

' If either trigger K+S or trigger .ILs has'operated, it is useful in some casesthat this trigger recharges via a charging gate T the capacitor Vit has tested -to the standard charge of thesame polarity as the char-ge i-t has detected. For the ycz-capacitor this is done in the interval of pulse B, for .the b-capacitor in the interval of pulse C, etc. and for the f-capacitor in the interval pulse A. The operation of the zero trigger K0 causes the rejection of the relevant signal, which in this case is due to the rejection of the signal element.

Y The transmission of an error repetition request signal, and the attendant blocking of the printer 22 (see FIG. l) and start of the repetition deviceZ- can be eiected immediately, if the so-called element repetition is applied, to operate at the end of the relevant 'signal or of the rele-` vant block of three signals, if signal or block repetition,

respectively, `are employedby connection from trigger RCZ'I to the repetition device 23 (see FIG. l).

After the test, if the zero trigger K0 has not operated, .all the capacitors a, b, c, etc. (twenty-one in number, one for each element of 3 seven element signals) belonging .to the scanning circuit of FIG.y 3 are connected to a set of'code triggers Kel throughL Kem having -av higher responsiveness than the'threshold triggers, notably at moment of pulse E1. The moments E1 and F1 are derived from triggers E and F via inhibition .gates, which suppress them if trigger K0 has operated (see FIG. 4).

The operation of the zero triggers K0 means that one of the twenty-one capacitors, eg. a, b,c an insruicient charge,vand according to the invention this capacitor must get the opportunity to receive, by a repetition of the signal, ,a suicient charge to change over its corresponding threshold triggers K+s or K s.

To thisend the working of the discharging gate 15 is suppressed by a blocking of triggers TE1 and TF1; while in the case of normal reception, this gate 15 is opened at moment of pulse F1 to discharge each of the twenty-one capacitors a, b, c, etc. Trigger K0 is periodically restored to normal by the moment of a pulse A.

' At moment of pulse El yan `applied voltage to the transfer gates 16 c-auses the charges of the twenty-one capacitors a, b, c, etc. to be shifted to the' code triggers Kel thnough Kem. This process too is suppressed if the zero trigger K0 has operated. So the device works as follows:

After an 21-units signal series ha-s been received .for

lthe iirst time, the twenty-one pairs of triggers K+s and K s have taken certa-in states,.which for the time being etc. a has,

4 will be supposed to be all clear lor sutiicient -l or states.

At the end of the lZl-units signal series,vwith the feedback paths or supplementary charging gate T, all the capacitors a, b, c etc..can'then be charged withrthe same voltage so -a's to have a clear, suicierrt, adequate, or complete voltage ,for charging the code`triggers Km through Km described later (for example: it may be 1/3 of the maximum value of U with undisturbed*transmission). In principle, however, the system 4also works without these supplemental charging gates T. At ythe moment of pulse E, all theV code triggers Kel through Kem are put in the lstates' conresponding to the charges lof the associated capacitors a, b, c, etc. inaconnection with which these code triggers Kd `through Kem have no fixed normal state.

. if at the first scanning one ofthe twenty-one elements s causes an inSuiiicientF-i-or -charge7 the triggers K+, and K s remain at normal/and change over separate which the vsignal is given once more.

zero trigger K'When the output terminals of allthe twenty-one condensers a, b, c, etc. are tested now, the whole ,2l-element signalseries is rejected. This results in a request for repetition, such as via conductor RQ from the code converter to the repetition device 23 in FIG. 1 upon detection in the code converter of a special RQ signal requesting said repetition, in consequence of ception, the charge of `capacitor a, which has been preserved `after thef first reception, lcan `be completed or altered, since no completing voltageV is received; back via `the supplemental charging gate' Tas longA as the corresponding Ks-trigger has not yet responded.

The circuit maybe so arranged that at a second'or next time, the code triggers which had been set-,the first time keep their charge.

In the diagram of the code` converter, FIG, 6, part of the column of code triggers KCl-Km is shown once more. At a control moment the code conversion in the code converter CC is carried out almost at once, i.e. immediately after the return of code triggers Kc, through Kem to the normal state; By'means of the new code, which may contain e.g. tive units, five of the seven code triggers viz. triggers Kcz through Kee, are set again, aftergwhich the signal can be passed to the printer sequentially.

This conversion is carried out by. groups of seven units in the 21-unit block. Y

FIG. 7 shows in a time diagram the .moments of al1 these operations. Notably the top shows the transmis- :sion of two blocks of three signals separatedfby a pauseA kto the sevenV code triggers orflip-iiops, and that at moment the conversion of the charges of .these rst seven code triggers in the tive-units code and the subsequent rpassing of the signal tothe printer must begin. It

lis assumed that/the code Yconversion and the folowing transmission of thefsignal to the printer, tobegin with a start element folowed by Vfive intelligence elements andV a stop element duringwhich the. code triggers are restored to normal have been etiected in interval a.

The discharge of the tirst seven capacitors'has finished atmomentfy. Y

The signalelement length ofthe printer is 20 ms. It can be seen fromV the drawing that the printing of the third letter hasr finished justy at `the end of the second block group time, at momentp. Y

While we have illustratedV and described what we regard to ybe the preferred embodiment of our invention, nevertheless it will 'be understood that such is merely exemplary and thatfnumerous modifications kand Vrearrangements may be made 4therein without departing from At the vsecond reelement signals between two stations, said system prising at each station: v

(A) receiving means for said signals,

(B) detecting means connected to said receiving means for discriminating between the mark elements and the space elements in each signal and for forming them into potentials of correspondingly different polarities,

(C) pulse Vgenerating means connected toy saidr discriminating means for. generating controlling pulses for each element of each signal,

(D) scanning means connected to said discriminating means and to said pulse generating Vmeans for scanning each element of each signal, said scanning means comprising:

(1),separate potential storing means for each said element of each signal,

(2) measuring means connected to each said storing means for measuring the potential level of .each stored element, .and v (3) a blocking means connected to said measur-V ing means for preventing the removal of the potentials in said storing means when at least one stored element has been measured'to be incomplete, I

V (E) means connected to. saidY storing'means for passing stored signal elements which have beenmeasured to be complete to anoutput circuit, Y

(F) means connected to said blocking means to request repetition of signals which contain at least one stored element which has/been measured to be incomplete, and Y (G) means at the other and remote station responsive to said repetition requesting means to repeat the signal incompletely stored to said storingl means to supplement the potential therein until it is measured to be'comple'te. l l e 2. A system according to claim l'wherein said multielement mark/ space signals comprise seven elements.

3. A system according .to claim 1 wherein the received signals are modulated on a high frequency carrier and said receiving means comprises a band pass filter.

4. A system according to claim 3 wherein said receiving means valso includes a limiter.

5. A systemY v according to claim 1 wherein said discriminatng means includes separate `tilters for said mark element and saidspaceelement.

6. A system accord-ing Vto claim 5 wherein said dis- COID- criminatjngmeans includes full Wave rectiiiers connected to each of said filters.

7. A system according to claim 1 wherein said pulse generating means includes a plurality of pulse generating triggers and a ring counter of triggers corresponding in number -to the number of elements to be stored in said scanning means.

8. A system according to claim 1 wherein said pulse generating means includes means for synchronizing said system in accordance with the leading edge of the irst element of each signal received.

9. A system according to claim 1 wherein said scanning means includes -a charging gate means connected between said storing means and said detecting means and connected to and controlled by said pulse generating means.

10. A system according to claim 9 wherein said charging gate means includes resistor land rectifier means.

11. A system according to claim 1 wherein said storing means includes separate storing means for each element of a plurality of signals in a group.

12. A system according to claim 1 wherein said mark and space elements have potentials of opposite polarity and said measuring means includes separate polarity determining means for each element of each signal.

13. A system according to claim 1 wherein said measnring meansis adjustably-responsive to different voltage levels. f

p14. A system according to claim 1 wherein said measuring meanscomprises `a. pair of threshold triggers.

f 15. vA system according to claim 14 wherein said measuring means comprises a testing gate connected between said Ystoring means and said lthreshold triggers.

f 16. A system laccording to claim-14 wherein said blocking means comprises aitriggermeans controlledI by said threshold triggers and said pulse generating means.

i 17. A system accordingA to clairn- 1 wherein -said scanning means includes means connected to said measuring means for supplementing the charge on saidstoring means after said signal element has been measured'and before it has been transferred to said passing means.

.y V18. A system according to claim 1 wherein saidvscanning means includes a transferring gate connected to said storing means for passing its stored element to said passing means. q v

19. A system according to claim 1 wherein each said storing means includes a condenser for storing the charge of each element of each signal lin said scanning means.

20. A system according to claim 1 wherein said scanning means includes means connected tol said storing means for discharging said storing means after the stored signal element has been transferred to said passing means.

21. A Vsystem Vaccording to claim 1 wherein said passing means includes a code convertingv means.

22. A system according to claim 21 wherein said code converting means includes a code trigger corresponding to each of the elements stored vin said scanning device. v

23. A system according to claim 1 wherein said storingmeans includes means for storing Ythe elements of agpluralityolfisignals in algroup, and wherein saidblocking meansoperates only after all of thesignal elements of said group have been stored for controlling said repetition requesting means and said passing means.

24. A telecommunication system for mark/ space multielement signalsbetween two stations comprising at each station: 1 v ,vl

(A) receiving means for said signals, Y Y (B) detecting means connected to said receiving means for discriminating between the mark elements and `the space elements in each signal and for forming them into f potentials of corresponding opposite (C);-pulse generating means connected to said detecting means for generatingk pulses for controlling each element of each signal and for generating additional controllingpulses, v f

(D) scanning means connectedto said detecting means and to said pulse generating means for scanning each element of each signal, said scanning means comprising:

(1) separate charging gate means for each element to be stored and controlled by said detecting means and pulse generating means,

(2) separate potential storing means connected to each charging gate means for storing each element of each received signal,

(3) measuring means connected to each said storing means for measuring the polarity and potential level of each stored element,

(4) a common blocking means connected to all said measuring means for preventing said additional controlling pulses in said pulse generating means from removing the potentials in said storing means when at least one stored element has been measured to be incomplete,

(5) separate transferring gate means connected to each storing means and said pulse generating means to be controlled by said additional controlling pulses for transferring said stored elements which have been measured to be complete from said storing means, and

agree,

a repetition of signals whichcontain'at least one` storedelement which has been measured tobe incomplete, and

Y (H) means at the other and remote station'respon- A siyeto said repetition requesting means to repeat i the signal incomplet'ely stored to` said storing means to supplement Vthe potential therein until it is measured to be complete.4

25. A system according to Y ning means includes means connected to said storing means and connected to and controlled by said measuring means for supplementing ythecharge on saidstoring-l means after the signal element in said storing means,V has been measured by said measuring means to be complete.

26.v A system according to claim 24 `wherein said scan-v ning means includes means for storing separate elements of a plurality of signals in a grouprof signalsfand said blocking `,means is responsive for controlling said repetition requesting means when one element in said groupl of-signals has beenV measured to be incomplete. ,l

` 27.1In a telecommuniation system`for multi-element code signals from .one station to another, each station having a transmitter, a receiver, and an automatic repetion device, wherein each element is detected vby said receiver as one of `two diilerent potentials; `the improvei ment comprising: Y

(A) means for storing each element potential as itis received, Y f

(B) testing means connected to said storing means responsive-to a predetermined potentialrlevelvof said stored element, y

(C) `means connected tosaid storingrm'eans lforremoving vthe potential of Vsaid element stored therein, and

(D) means connected to said testing-means fory preclaim 24 wherein said scan-` venting the potential removing means from operating, and for operating said repetition device to repeatfra `below-level testedsignal element for supple- K inenting-.the potential on said storing means until said Vpredetermined level isvreached andv said removing means; is operated.J 28; A system according to claim 27 wherein said differentpotential levels have opposite polarity, and wherein s'aid improvement includes: i Y

(E) means connected between saidr storing means and saidrtesting means for determining the polarity of saidY stored element. c 29,'.v Asystem according to claim 27V including:

(F)'means lconnected to said storing means for re- Y sponding to the elements stored therein, and (G) means `connected to saidtesting means for permitting said responding means to operate when said potential of the stored element is at least Vat said predetermined level.f 30. In a telecommunication system for multi-element code signals from one station to another, each station having a transmittera receiver, andan automatic repetitiondevice, wherein each `element is detected by said receiver as one of two diierent'potentials; the improvement comprising:

(A) meansfor storingeach elementpotential as it is received, Y (B) testing means connected to said :storing means responsive to a predetermined potential levell of said stored-element, (C) means connected to said storing vmeans for responding to said elements stored therein, and (D) meansv connected to said testing means for permitting said responding Ameans. to operate only when said potential of said rstoredelement is at least at said predetermined-level, and for preventing the removal of said potential from said storing means until said predetermined level has been built References Cited by the Examiner Y v UNITED STATES `PATENTS 9/57 Van Duuren 178--23 X 2,970,189 Y 1/61 Van Dalen et al. 178--23 2,988,596 6/61 Van Dalen 178-23 2,995,626 8/61Y Van Duuren 17823 MALCOLM A.;MORRISON, Primary Examiner.

5 NEWTON N. LOVEWELL, Examiner. 

1. A TELECOMMUNICATION SYSTEM FOR MARK-SPACE MULTIELEMENT SIGNALS BETWEEN TWO STATIONS, SAID SYSTEM COMPRISING AT EACH STATION: (A) RECEIVING MEANS FOR SAID SIGNALS, (B) DETECTING MEANS CONNECTED TO SAID RECEIVING MEANS FOR DISCRIMINATING BETWEEN THE MARK ELEMENTS AND THE SPACE ELEMENTS IN EACH SIGNAL AND FOR FORMING THEM INTO POTENTIALS OF CORRESPONDINGLY DIFFERENT POLARITIES, (C) PULSE GENERATING MEANS CONNECTED TO SAID DISCRIMINATING MEANS FOR GENERATING CONTROLLING PULSES FOR EACH ELEMENT OF SAID SIGNAL, (D) SCANNING MEANS CONNECTED TO SAID DISCRIMINATING MEANS AND TO SAID PULSE GENERATING MEANS FOR SCANNING EACH ELEMENT OF EACH SIGNAL, SAID SCANNING MEANS COMPRISING: (1) SEPARATE POTENTIAL STORING MEANS FOR EACH SAID ELEMENT OF EACH SIGNAL, (2) MEASURING MEANS CONNECTED TO EACH SAID STORING MEANS FOR MEASURING THE POTENTIAL LEVEL OF EACH STORED ELEMENT, AND (3) A BLOCKING MEANS CONNECTED TO SAID MEASURING MEANS FOR PREVENTING THE REMOVAL OF THE POTENTIALS IN SAID STORING MEANS WHEN AT LEAST ONE STORED ELEMENT HAS BEEN MEASURED TO BE INCOMPLETE, (E) MEANS CONNECTED TO SAID STORING MEANS FOR PASSING STORED SIGNAL ELEMENTS WHICH HAVE BEEN MEASURED TO BE COMPLETE TO AN OUTPUT CIRCUIT, (F) MEANS CONNECTED TO SAID BLOCKING MEANS TO REQUEST REPETITION OF SIGNALS WHICH CONTAIN AT LEAST ONE STORED ELEMENT WHICH HAS BEEN MEASURED TO BE INCOMPLETE, AND (G) MEANS AT THE OTHER AND REMOTE STATION RESPONSIVE TO SAID REPETITION REQUESTING MEANS TO REPEAT THE SIGNAL INCOMPLETELY STORED TO SAID STORING MEANS TO SUPPLEMENT THE POTENTIAL THEREIN UNTIL IT IS MEASURED TO BE COMPLETE. 